The invention relates to a method for fuel proportioning in a gas-powered combustion engine. It also relates to a device for such fuel pro portioning.
Gas intended for driving a gas engine is usually stored at high pressure. After pressure reduction in one or more stages, the as is mixed with air in correct proportions for good combustion. A larger or smaller quantity of gas and air is supplied, depending on the load.
Mixing of gas and air usually takes place in a mechanical type of mixer which has to be set for the particular quality of gas by applying a manual basic setting for maintaining the intended ratio between gas and air during load variation. When steady conditions prevail, the desired good combustion result is achieved, but if the gas proportion changes, e.g. because of pressure change, gas quality change or any other reason, an adjustment is required to restore the correct proportions of gas and air and hence achieve the intended good combustion. A need for adjustment of this kind may arise, for example, from refuelling. There have also been found to be relatively large differences in the quality of gas fuel available in different geographical areas. This means that the manufacture of gas engines has to include individual adaptation of each engine according to the market or geographical area for which it is intended. The way gas engines are often used means that they are always refuelled from the same filling stations. In such cases it is sufficient, at least for a certain time, to abide by the manufacturer's original setting, but the fact that without adjustment the engine cannot be used in other geographical areas or use fuel from other fuel filling stations does of course limit the possibilities of using such an engine in, for example, a vehicle intended to travel considerable distances.
From the operating point of view it would be a great advantage if adjustment could be effected automatically. This would not only mean that any carelessness or forgetfulness on the occasion of refuelling need not cause bad combustion but also that a difficult operation could be obviated. It would thus be easier for gas-powered vehicles to use fuel from different filling stations, thereby facilitating lengthy journeys.
Like a diesel engine, a gas-powered combustion engine usually operates with excess air, i.e. with an air/fuel ratio greater than 1.0. This means that the oxygen content of the exhaust gases cannot be measured by means of the conventional type of .lambda. probe which is usually employed for gasoline engines to aim at a value of about 1.0, since what is required is a different type of .lambda. probe which can monitor higher .lambda. values. As such .lambda. probes have now reached the market, various designs have been proposed whereby continuous adaptation and correction of the air/fuel ratio takes place in the actual mixer on the basis of signals from the .lambda. sensor.
Also known is the use of electronically controlled gas injection whereby a control unit calculates and proportions the required gas quantity on the basis of various operating data.
A disadvantage of these solutions is that they are relatively sensitive and require a great deal of maintenance.